Method for controlling a hybrid powertrain system based upon hydraulic pressure and clutch reactive torque capacity

ABSTRACT

A powertrain system includes an engine coupled to an electro-mechanical transmission to transfer power between the engine and a plurality of torque generating machines and an output member. The transmission is operative in one of a plurality of operating range states through selective application of torque transfer clutches and the engine is operatively coupled to a main hydraulic pump to supply pressurized fluid to a hydraulic circuit operative to apply the torque transfer clutches. A method for controlling the powertrain system includes determining an output torque request to the output member, determining a pressure output of the main hydraulic pump based upon an engine input speed, calculating a clutch reactive torque capacity for each applied torque transfer clutch based upon the pressure output of the main hydraulic pump, and determining a preferred engine input speed to achieve the clutch reactive torque capacity to meet the output torque request to the output member.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No.60/985,632, filed on Nov. 05, 2007 which is hereby incorporated hereinby reference.

TECHNICAL FIELD

This disclosure pertains to control systems for hybrid powertrainsystems.

BACKGROUND

The statements in this section merely provide background informationrelated to the present disclosure and may not constitute prior art.

Known hybrid powertrain architectures can include multipletorque-generative devices, including internal combustion engines andnon-combustion machines, e.g., electric machines, which transmit torquethrough a transmission device to an output member. One exemplary hybridpowertrain includes a two-mode, compound-split, electromechanicaltransmission which utilizes an input member for receiving tractivetorque from a prime mover power source, preferably an internalcombustion engine, and an output member. The output member can beoperatively connected to a driveline for a motor vehicle fortransmitting tractive torque thereto. Machines, operative as motors orgenerators, can generate torque inputs to the transmission independentlyof a torque input from the internal combustion engine. The Machines maytransform vehicle kinetic energy transmitted through the vehicledriveline to energy that is storable in an energy storage device. Acontrol system monitors various inputs from the vehicle and the operatorand provides operational control of the hybrid powertrain, includingcontrolling transmission operating state and gear shifting, controllingthe torque-generative devices, and regulating the power interchangeamong the energy storage device and the machines to manage outputs ofthe transmission, including torque and rotational speed.

SUMMARY

A powertrain system includes an engine coupled to an electro-mechanicaltransmission to transfer power between the engine and a plurality oftorque generating machines and an output member. The transmission isoperative in one of a plurality of operating range states throughselective application of torque transfer clutches and the engine isoperatively coupled to a main hydraulic pump to supply pressurized fluidto a hydraulic circuit operative to apply the torque transfer clutches.A method for controlling the powertrain system includes determining anoutput torque request to the output member, determining a pressureoutput of the main hydraulic pump based upon an engine input speed,calculating a clutch reactive torque capacity for each applied torquetransfer clutch based upon the pressure output of the main hydraulicpump, and determining a preferred engine input speed to achieve theclutch reactive torque capacity to meet the output torque request to theoutput member.

BRIEF DESCRIPTION OF THE DRAWINGS

One or more embodiments will now be described, by way of example, withreference to the accompanying drawings, in which:

FIG. 1 is a schematic diagram of an exemplary hybrid powertrain, inaccordance with the present disclosure;

FIG. 2 is a schematic diagram of an exemplary architecture for a controlsystem and hybrid powertrain, in accordance with the present disclosure;

FIGS. 3-7 are schematic flow diagrams of a control scheme, in accordancewith the present disclosure; and

FIGS. 8 and 9 are datagraphs, in accordance with the present disclosure.

DETAILED DESCRIPTION

Referring now to the drawings, wherein the showings are for the purposeof illustrating certain exemplary embodiments only and not for thepurpose of limiting the same, FIGS. 1 and 2 depict an exemplary hybridpowertrain system. The exemplary hybrid powertrain system in accordancewith the present disclosure is depicted in FIG. 1, comprising atwo-mode, compound-split, electromechanical hybrid transmission 10operatively connected to an engine 14 and torque generating machinescomprising first and second electric machines (‘MG-A’) 56 and (‘MG-B’)72. The engine 14 and first and second electric machines 56 and 72 eachgenerate mechanical power which can be transferred to the transmission10. The power generated by the engine 14 and the first and secondelectric machines 56 and 72 and transferred to the transmission 10 isdescribed in terms of input and motor torques, referred to herein asT_(I), T_(A), and T_(B) respectively, and speed, referred to herein asN_(I), N_(A), and N_(B), respectively.

The exemplary engine 14 comprises a multi-cylinder internal combustionengine selectively operative in several states to transfer torque to thetransmission 10 via an input shaft 12, and can be either aspark-ignition or a compression-ignition engine. The engine 14 includesa crankshaft (not shown) operatively coupled to the input shaft 12 ofthe transmission 10. A rotational speed sensor 11 monitors rotationalspeed of the input shaft 12. Power output from the engine 14, comprisingrotational speed and engine torque, can differ from the input speedN_(I) and the input torque T_(I) to the transmission 10 due to placementof torque-consuming components on the input shaft 12 between the engine14 and the transmission 10, e.g., a hydraulic pump 88 and/or a torquemanagement device (not shown).

The exemplary transmission 10 comprises three planetary-gear sets 24, 26and 28, and four selectively engageable torque-transferring devices,i.e., clutches C1 70, C2 62, C3 73, and C4 75. As used herein, clutchesrefer to any type of friction torque transfer device including single orcompound plate clutches or packs, band clutches, and brakes, forexample. The hydraulic pump 88 supplies pressurized hydraulic fluid to ahydraulic control circuit (‘HYD’) 42 that is preferably controlled by atransmission control module (hereafter ‘TCM’) 17 operative to controlclutch states. Clutches C2 62 and C4 75 preferably comprisehydraulically-applied rotating friction clutches. Clutches Cl 70 and C373 preferably comprise hydraulically-controlled stationary devices thatcan be selectively grounded to a transmission case 68. Each of theclutches C1 70, C2 62, C3 73, and C4 75 is preferably hydraulicallyapplied, selectively receiving pressurized hydraulic fluid via thehydraulic control circuit 42. Clutch pressure, and thus clutch reactivetorque is based upon and limited by the hydraulic pressure in thehydraulic control circuit 42. The operation of the hydraulic controlcircuit 42 including the hydraulic pump 88 to generate hydraulicpressure is described hereinbelow with reference to FIG. 8.

The first and second electric machines 56 and 72 preferably comprisethree-phase AC machines, each including a stator (not shown) and a rotor(not shown), and respective resolvers 80 and 82. The motor stator foreach machine is grounded to an outer portion of the transmission case68, and includes a stator core with coiled electrical windings extendingtherefrom. The rotor for the first electric machine 56 is supported on ahub plate gear that is operatively attached to shaft 60 via the secondplanetary gear set 26. The rotor for the second electric machine 72 isfixedly attached to a sleeve shaft hub 66.

Each of the resolvers 80 and 82 preferably comprises a variablereluctance device including a resolver stator (not shown) and a resolverrotor (not shown). The resolvers 80 and 82 are appropriately positionedand assembled on respective ones of the first and second electricmachines 56 and 72. Stators of respective ones of the resolvers 80 and82 are operatively connected to one of the stators for the first andsecond electric machines 56 and 72. The resolver rotors are operativelyconnected to the rotor for the corresponding first and second electricmachines 56 and 72. Each of the resolvers 80 and 82 is signally andoperatively connected to a transmission power inverter control module(hereafter ‘TPIM’) 19, and each senses and monitors rotational positionof the resolver rotor relative to the resolver stator, thus monitoringrotational position of respective ones of first and second electricmachines 56 and 72. Additionally, the signals output from the resolvers80 and 82 are interpreted to provide the rotational speeds for first andsecond electric machines 56 and 72, i.e., N_(A) and N_(B), respectively.

The transmission 10 includes an output member 64, e.g. a shaft, which isoperably connected to a driveline 90 for a vehicle (not shown), toprovide output power to the driveline 90 that is transferred to vehiclewheels 93, one of which is shown in FIG. 1. The output power at theoutput member 64 is characterized in terms of an output rotational speedN_(O) and an output torque T_(O). A transmission output speed sensor 84monitors rotational speed and rotational direction of the output member64. Each of the vehicle wheels 93 is preferably equipped with a frictionbrake 94 and a sensor (not shown) adapted to monitor wheel speed, theoutput of which is monitored by a control module of a distributedcontrol module system described with respect to FIG. 2, to determinevehicle speed, and absolute and relative wheel speeds for brakingcontrol, traction control, and vehicle acceleration management.

The input torque from the engine 14 and the motor torques from the firstand second electric machines 56 and 72 (T_(I), T_(A), and T_(B)respectively) are generated as a result of energy conversion from fuelor electrical potential stored in an electrical energy storage device(hereafter ‘ESD’) 74. The ESD 74 is high voltage DC-coupled to the TPIM19 via DC transfer conductors 27. The transfer conductors 27 include acontactor switch 38. When the contactor switch 38 is closed, undernormal operation, electric current can flow between the ESD 74 and theTPIM 19. When the contactor switch 3 8 is opened electric current flowbetween the ESD 74 and the TPIM 19 is interrupted. The TPIM 19 transmitselectrical power to and from the first electric machine 56 by transferconductors 29, and the TPIM 19 similarly transmits electrical power toand from the second electric machine 72 by transfer conductors 31 tomeet the torque commands for the first and second electric machines 56and 72 in response to the motor torque commands T_(A) and T_(B).Electrical current is transmitted to and from the ESD 74 in accordancewith whether the ESD 74 is being charged or discharged.

The TPIM 19 includes the pair of power inverters (not shown) andrespective motor control modules (not shown) configured to receive themotor torque commands and control inverter states therefrom forproviding motor drive or regeneration functionality to meet thecommanded motor torques T_(A) and T_(B). The power inverters compriseknown complementary three-phase power electronics devices, and eachincludes a plurality of insulated gate bipolar transistors (not shown)for converting DC power from the ESD 74 to AC power for poweringrespective ones of the first and second electric machines 56 and 72, byswitching at high frequencies. The insulated gate bipolar transistorsform a switch mode power supply configured to receive control commands.There is typically one pair of insulated gate bipolar transistors foreach phase of each of the three-phase electric machines. States of theinsulated gate bipolar transistors are controlled to provide motor drivemechanical power generation or electric power regenerationfunctionality. The three-phase inverters receive or supply DC electricpower via DC transfer conductors 27 and transform it to or fromthree-phase AC power, which is conducted to or from the first and secondelectric machines 56 and 72 for operation as motors or generators viatransfer conductors 29 and 31 respectively.

FIG. 2 is a schematic block diagram of the distributed control modulesystem. The elements described hereinafter comprise a subset of anoverall vehicle control architecture, and provide coordinated systemcontrol of the exemplary hybrid powertrain described in FIG. 1. Thedistributed control module system synthesizes pertinent information andinputs, and executes algorithms to control various actuators to meetcontrol objectives, including objectives related to fuel economy,emissions, performance, drivability, and protection of hardware,including batteries of ESD 74 and the first and second electric machines56 and 72. The distributed control module system includes an enginecontrol module (hereafter ‘ECM’) 23, the TCM 17, a battery pack controlmodule (hereafter ‘BPCM’) 21, and the TPIM 19. A hybrid control module(hereafter ‘HCP’) 5 provides supervisory control and coordination of theECM 23, the TCM 17, the BPCM 21, and the TPIM 19. A user interface(‘UI’) 13 is operatively connected to a plurality of devices throughwhich a vehicle operator controls or directs operation of theelectromechanical hybrid powertrain system. The devices include anaccelerator pedal 113 (‘AP’), an operator brake pedal 112 (‘BP’), atransmission gear selector 114 (‘PRNDL’), and a vehicle speed cruisecontrol (not shown). The transmission gear selector 114 may have adiscrete number of operator-selectable positions, including therotational direction of the output member 64 to enable one of a forwardand a reverse direction.

The aforementioned control modules communicate with other controlmodules, sensors, and actuators via a local area network (hereafter‘LAN’) bus 6. The LAN bus 6 allows for structured communication ofstates of operating parameters and actuator command signals between thevarious control modules. The specific communication protocol utilized isapplication-specific. The LAN bus 6 and appropriate protocols providefor robust messaging and multi-control module interfacing between theaforementioned control modules, and other control modules providingfunctionality including e.g., antilock braking, traction control, andvehicle stability. Multiple communications buses may be used to improvecommunications speed and provide some level of signal redundancy andintegrity. Communication between individual control modules can also beeffected using a direct link, e.g., a serial peripheral interface(‘SPI’) bus (not shown).

The HCP 5 provides supervisory control of the hybrid powertrain, servingto coordinate operation of the ECM 23, TCM 17, TPIM 19, and BPCM 21.Based upon various input signals from the user interface 13 and thehybrid powertrain, including the ESD 74, the HCP 5 determines anoperator torque request, an output torque command, an engine inputtorque command, clutch torque(s) for the applied torque-transferclutches C1 70, C2 62, C3 73, C4 75 of the transmission 10, and themotor torque commands T_(A) and T_(B) for the first and second electricmachines 56 and 72.

The ECM 23 is operatively connected to the engine 14, and functions toacquire data from sensors and control actuators of the engine 14 over aplurality of discrete lines, shown for simplicity as an aggregatebi-directional interface cable 35. The ECM 23 receives the engine inputtorque command from the HCP 5. The ECM 23 determines the actual engineinput torque, T_(I), provided to the transmission 10 at that point intime based upon monitored engine speed and load, which is communicatedto the HCP 5. The ECM 23 monitors input from the rotational speed sensor11 to determine the engine input speed to the input shaft 12, whichtranslates to the transmission input speed, N_(I). The ECM 23 monitorsinputs from sensors (not shown) to determine states of other engineoperating parameters including, e.g., a manifold pressure, enginecoolant temperature, ambient air temperature, and ambient pressure. Theengine load can be determined, for example, from the manifold pressure,or alternatively, from monitoring operator input to the acceleratorpedal 113. The ECM 23 generates and communicates command signals tocontrol engine actuators, including, e.g., fuel injectors, ignitionmodules, and throttle control modules, none of which are shown.

The TCM 17 is operatively connected to the transmission 10 and monitorsinputs from sensors (not shown) to determine states of transmissionoperating parameters. The TCM 17 generates and communicates commandsignals to control the transmission 10, including controlling thehydraulic circuit 42. Inputs from the TCM 17 to the HCP 5 includeestimated clutch torques for each of the clutches, i.e., C1 70, C2 62,C3 73, and C4 75, and rotational output speed, N_(O), of the outputmember 64. Other actuators and sensors may be used to provide additionalinformation from the TCM 17 to the HCP 5 for control purposes. The TCM17 monitors inputs from pressure switches (not shown) and selectivelyactuates pressure control solenoids (not shown) and shift solenoids (notshown) of the hydraulic circuit 42 to selectively actuate the variousclutches C1 70, C2 62, C3 73, and C4 75 to achieve various transmissionoperating range states, as described hereinbelow.

The BPCM 21 is signally connected to sensors (not shown) to monitor theESD 74, including states of electrical current and voltage parameters,to provide information indicative of parametric states of the batteriesof the ESD 74 to the HCP 5. The parametric states of the batteriespreferably include battery state-of-charge, battery voltage, batterytemperature, and available battery power, referred to as a range P_(BAT)_(—) _(MIN) to P_(BAT) _(—) _(MAX).

A brake control module (hereafter ‘BrCM’) 22 is operatively connected tofriction brakes 94 on each of the vehicle wheels 93. The BrCM 22monitors the operator input to the brake pedal 112 and generates controlsignals to control the friction brakes 94 and sends a control signal tothe HCP 5 to operate the transmission 10 and the first and secondelectric machines 56 and 72 based thereon. Braking preferably comprisesa blending of friction braking and regenerative braking. Frictionbraking is effected by applying the friction brakes 94. Regenerativebraking is effected through the driveline 90 by selectively applying oneof the clutches and controlling the first and second electric machines56 and 72 to react torque transferred from the driveline 90 through thepower inverters and respective motor control modules to meet thecommanded motor torques T_(A) and T_(B).

Each of the control modules ECM 23, TCM 17, TPIM 19, BPCM 21, and BrCM22 is preferably a general-purpose digital computer comprising amicroprocessor or central processing unit, storage mediums comprisingread only memory (‘ROM’), random access memory (‘RAM’), electricallyprogrammable read only memory (‘EPROM’), a high speed clock, analog todigital (‘A/D’) and digital to analog (‘D/A’) circuitry, andinput/output circuitry and devices (‘I/O’) and appropriate signalconditioning and buffer circuitry. Each of the control modules has a setof control algorithms, comprising resident program instructions andcalibrations stored in one of the storage mediums and executed toprovide the respective functions of each computer. Information transferbetween the control modules is preferably accomplished using the LAN bus6 and serial peripheral interface buses. The control algorithms areexecuted during preset loop cycles such that each algorithm is executedat least once each loop cycle. Algorithms stored in the non-volatilememory devices are executed by one of the central processing units tomonitor inputs from the sensing devices and execute control anddiagnostic routines to control operation of the actuators, using presetcalibrations. Loop cycles are executed at regular intervals, for exampleeach 3.125, 6.25, 12.5, 25 and 100 milliseconds during ongoing operationof the hybrid powertrain. Alternatively, algorithms may be executed inresponse to the occurrence of an event.

The exemplary hybrid powertrain selectively operates in one of severalstates that can be described in terms of engine states comprising one ofan engine-on state (‘ON’) and an engine-off state (‘OFF’), andtransmission operating range states comprising a plurality of fixedgears and continuously variable operating modes, described withreference to Table 1, below.

TABLE 1 Engine Transmission Operating Applied Description State RangeState Clutches M1_Eng_Off OFF EVT Mode 1 C1 70 M1_Eng_On ON EVT Mode 1C1 70 G1 ON Fixed Gear Ratio 1 C1 70 C4 75 G2 ON Fixed Gear Ratio 2 C170 C2 62 M2_Eng_Off OFF EVT Mode 2 C2 62 M2_Eng_On ON EVT Mode 2 C2 62G3 ON Fixed Gear Ratio 3 C2 62 C4 75 G4 ON Fixed Gear Ratio 4 C2 62 C373

Each of the transmission operating range states is described in thetable and indicates which of the specific clutches C1 70, C2 62, C3 73,and C4 75 are applied for each of the operating range states. A firstcontinuously variable mode, i.e., EVT Mode 1, or M1, is selected byapplying clutch C1 70 only in order to “ground” the outer gear member ofthe third planetary gear set 28. The engine state can be one of ON(‘M1_Eng_On’) or OFF (‘M1_Eng_Off’). A second continuously variablemode, i.e., EVT Mode 2, or M2, is selected by applying clutch C2 62 onlyto connect the shaft 60 to the carrier of the third planetary gear set28. The engine state can be one of ON (‘M2_Eng_On’) or OFF(‘M2_Eng_Off’). For purposes of this description, when the engine stateis OFF, the engine input speed is equal to zero revolutions per minute(‘RPM’), i.e., the engine crankshaft is not rotating. A fixed gearoperation provides a fixed ratio operation of input-to-output speed ofthe transmission 10, i.e., N_(I)/N_(O). A first fixed gear operation(‘G1’) is selected by applying clutches C1 70 and C4 75. A second fixedgear operation (‘G2’) is selected by applying clutches C1 70 and C2 62.A third fixed gear operation (‘G3’) is selected by applying clutches C262 and C4 75. A fourth fixed gear operation (‘G4’) is selected byapplying clutches C2 62 and C3 73. The fixed ratio operation ofinput-to-output speed increases with increased fixed gear operation dueto decreased gear ratios in the planetary gears 24, 26, and 28. Therotational speeds of the first and second electric machines 56 and 72,N_(A) and N_(B) respectively, are dependent on internal rotation of themechanism as defined by the clutching and are proportional to the inputspeed measured at the input shaft 12.

In response to operator input via the accelerator pedal 113 and brakepedal 112 as captured by the user interface 13, the HCP 5 and one ormore of the other control modules determine torque commands to controlthe torque generating devices comprising the engine 14 and the first andsecond electric machines 56 and 72 to meet the operator torque requestat the output member 64 and transferred to the driveline 90. Based uponinput signals from the user interface 13 and the hybrid powertrainincluding the ESD 74, the HCP 5 determines the operator torque request,the output torque command from the transmission 10 to the driveline 90,the input torque from the engine 14, clutch torques for thetorque-transfer clutches C1 70, C2 62, C3 73, C4 75 of the transmission10; and the motor torques for the first and second electric machines 56and 72, respectively, as is described hereinbelow.

Final vehicle acceleration can be affected by other factors including,e.g., road load, road grade, and vehicle mass. The engine state and thetransmission operating range state are determined based upon operatingcharacteristics of the hybrid powertrain. This includes the operatortorque request communicated through the accelerator pedal 113 and brakepedal 112 to the user interface 13 as previously described. Thetransmission operating range state and the engine state may bepredicated on a hybrid powertrain torque demand caused by a command tooperate the first and second electric machines 56 and 72 in anelectrical energy generating mode or in a torque generating mode. Thetransmission operating range state and the engine state can bedetermined by an optimization algorithm or routine which determinesoptimum system efficiency based upon operator demand for power, batterystate of charge, and energy efficiencies of the engine 14 and the firstand second electric machines 56 and 72. The control system managestorque inputs from the engine 14 and the first and second electricmachines 56 and 72 based upon an outcome of the executed optimizationroutine, and system efficiencies are optimized thereby, to manage fueleconomy and battery charging. Furthermore, operation can be determinedbased upon a fault in a component or system. The HCP 5 monitors thetorque generating machines, and determines the power output from thetransmission 10 at output member 64 that is required to meet theoperator torque request while meeting other powertrain operatingdemands, e.g., charging the ESD 74. As should be apparent from thedescription above, the ESD 74 and the first and second electric machines56 and 72 are electrically-operatively coupled for power flowtherebetween. Furthermore, the engine 14, the first and second electricmachines 56 and 72, and the electromechanical transmission 10 aremechanically-operatively coupled to transfer power therebetween togenerate a power flow to the output member 64.

FIG. 3 shows a control system architecture for controlling and managingsignal flow in a hybrid powertrain system having multiple torquegenerating devices, described hereinbelow with reference to the hybridpowertrain system of FIGS. 1 and 2, and residing in the aforementionedcontrol modules in the form of executable algorithms and calibrations.The control system architecture is applicable to alternative hybridpowertrain systems having multiple torque generating devices, including,e.g., a hybrid powertrain system having an engine and a single electricmachine, a hybrid powertrain system having an engine and multipleelectric machines. Alternatively, the hybrid powertrain system canutilize non-electric torque-generative machines and energy storagesystems, e.g., hydraulic-mechanical hybrid transmissions (not shown).

In operation, the operator inputs to the accelerator pedal 113 and thebrake pedal 112 are monitored to determine the operator torque request.The operator inputs to the accelerator pedal 113 and the brake pedal 112comprise individually determinable operator torque request inputsincluding an immediate accelerator output torque request (‘Output TorqueRequest Accel Immed’), a predicted accelerator output torque request(‘Output Torque Request Accel Prdtd’), an immediate brake output torquerequest (‘Output Torque Request Brake Immed’), a predicted brake outputtorque request (‘Output Torque Request Brake Prdtd’) and an axle torqueresponse type (‘Axle Torque Response Type’). As used herein, the term‘accelerator’ refers to an operator request for forward propulsionpreferably resulting in increasing vehicle speed over the presentvehicle speed, when the operator selected position of the transmissiongear selector 114 commands operation of the vehicle in the forwarddirection. The terms ‘deceleration’ and ‘brake’ refer to an operatorrequest preferably resulting in decreasing vehicle speed from thepresent vehicle speed. The immediate accelerator output torque request,the predicted accelerator output torque request, the immediate brakeoutput torque request, the predicted brake output torque request, andthe axle torque response type are individual inputs to the controlsystem. Additionally, operation of the engine 14 and the transmission 10are monitored to determine the input speed (‘Ni’) and the output speed(‘No’).

The immediate accelerator output torque request is determined based upona presently occurring operator input to the accelerator pedal 113, andcomprises a request to generate an immediate output torque at the outputmember 64 preferably to accelerate the vehicle. The predictedaccelerator output torque request is determined based upon the operatorinput to the accelerator pedal 113 and comprises an optimum or preferredoutput torque at the output member 64. The predicted accelerator outputtorque request is preferably equal to the immediate accelerator outputtorque request during normal operating conditions, e.g., when any one ofantilock braking, traction control, or vehicle stability is not beingcommanded. When any one of antilock braking, traction control or vehiclestability is being commanded the predicted accelerator output torquerequest remains the preferred output torque with the immediateaccelerator output torque request being decreased in response to outputtorque commands related to the antilock braking, traction control, orvehicle stability control.

The immediate brake output torque request is determined based upon apresently occurring operator input to the brake pedal 112, and comprisesa request to generate an immediate output torque at the output member 64to effect a reactive torque with the driveline 90 which preferablydecelerates the vehicle. The predicted brake output torque requestcomprises an optimum or preferred brake output torque at the outputmember 64 in response to an operator input to the brake pedal 112subject to a maximum brake output torque generated at the output member64 allowable regardless of the operator input to the brake pedal 112. Inone embodiment the maximum brake output torque generated at the outputmember 64 is limited to −0.2 g. The predicted brake output torquerequest can be phased out to zero when vehicle speed approaches zeroregardless of the operator input to the brake pedal 112. When commandedby the operator, there can be operating conditions under which thepredicted brake output torque request is set to zero, e.g., when theoperator setting to the transmission gear selector 114 is set to areverse gear, and when a transfer case (not shown) is set to afour-wheel drive low range.

A strategic control scheme (‘Strategic Control’) 310 determines apreferred input speed (‘Ni_Des’) and a preferred engine state andtransmission operating range state (‘Hybrid Range State Des’) based uponthe output speed and the operator torque request and based upon otheroperating parameters of the hybrid powertrain, including battery powerlimits and response limits of the engine 14, the transmission 10, andthe first and second electric machines 56 and 72. The predictedaccelerator output torque request and the predicted brake output torquerequest are input to the strategic control scheme 310. The strategiccontrol scheme 310 is preferably executed by the HCP 5 during each 100ms loop cycle and each 25 ms loop cycle. The desired operating rangestate for the transmission 10 and the desired input speed from theengine 14 to the transmission 10 are inputs to the shift execution andengine start/stop control scheme 320.

The shift execution and engine start/stop control scheme 320 commandschanges in the transmission operation (‘Transmission Commands’)including changing the operating range state based upon the inputs andoperation of the powertrain system. This includes commanding executionof a change in the transmission operating range state if the preferredoperating range state is different from the present operating rangestate by commanding changes in application of one or more of theclutches C1 70, C2 62, C3 73, and C4 75 and other transmission commands.The present operating range state (‘Hybrid Range State Actual’) and aninput speed profile (‘Ni_Prof’) can be determined. The input speedprofile is an estimate of an upcoming input speed and preferablycomprises a scalar parametric value that is a targeted input speed forthe forthcoming loop cycle. The engine operating commands and theoperator torque request are based upon the input speed profile during atransition in the operating range state of the transmission.

A tactical control scheme (‘Tactical Control and Operation’) 330 isexecuted during one of the control loop cycles to determine enginecommands (‘Engine Commands’) for operating the engine 14, including apreferred input torque from the engine 14 to the transmission 10 basedupon the output speed, the input speed, and the operator torque requestcomprising the immediate accelerator output torque request, thepredicted accelerator output torque request, the immediate brake outputtorque request, the predicted brake output torque request, the axletorque response type, and the present operating range state for thetransmission. The engine commands also include engine states includingone of an all-cylinder operating state and a cylinder deactivationoperating state wherein a portion of the engine cylinders aredeactivated and unfueled, and engine states including one of a fueledstate and a fuel cutoff state. An engine command comprising thepreferred input torque of the engine 14 and the present input torque(‘Ti’) reacting between the engine 14 and the input member 12 arepreferably determined in the ECM 23. Clutch reactive torques (‘Tc1’) foreach of the clutches C1 70, C2 62, C3 73, and C4 75, including thepresently applied clutches and the non-applied clutches are estimated,preferably in the TCM 17.

An output and motor torque determination scheme (‘Output and MotorTorque Determination’) 340 is executed to determine the preferred outputtorque from the powertrain (‘To_cmd’). This includes determining motortorque commands (‘T_(A)’, ‘T_(B)’) to transfer a net commanded outputtorque to the output member 64 of the transmission 10 that meets theoperator torque request, by controlling the first and second electricmachines 56 and 72 in this embodiment. The immediate accelerator outputtorque request, the immediate brake output torque request, the presentinput torque from the engine 14 and the estimated applied clutchtorque(s), the present operating range state of the transmission 10, theinput speed, the input speed profile, and the axle torque response typeare inputs. The output and motor torque determination scheme 340executes to determine the motor torque commands during each iteration ofone of the loop cycles. The output and motor torque determination scheme340 includes algorithmic code which is regularly executed during the6.25 ms and 12.5 ms loop cycles to determine the preferred motor torquecommands.

The hybrid powertrain is controlled to transfer the output torque to theoutput member 64 to react with the driveline 90 to generate tractivetorque at wheel(s) 93 to forwardly propel the vehicle in response to theoperator input to the accelerator pedal 113 when the operator selectedposition of the transmission gear selector 114 commands operation of thevehicle in the forward direction. Similarly, the hybrid powertrain iscontrolled to transfer the output torque to the output member 64 toreact with the driveline 90 to generate tractive torque at wheel(s) 93to propel the vehicle in a reverse direction in response to the operatorinput to the accelerator pedal 113 when the operator selected positionof the transmission gear selector 114 commands operation of the vehiclein the reverse direction. Preferably, propelling the vehicle results invehicle acceleration so long as the output torque is sufficient toovercome external loads on the vehicle, e.g., due to road grade,aerodynamic loads, and other loads.

FIG. 4 details signal flow in the strategic optimization control scheme310, which includes a strategic manager 220, an operating range stateanalyzer 260, and a state stabilization and arbitration block 280 todetermine the preferred input speed (‘Ni_Des’) and the preferredtransmission operating range state (‘Hybrid Range State Des’). Thestrategic manager (‘Strategic Manager’) 220 monitors the output speedN_(O), the predicted accelerator output torque request (‘Output TorqueRequest Accel Prdtd’), the predicted brake output torque request(‘Output Torque Request Brake Prdtd’), and available battery powerP_(BAT) _(—) _(MIN) to P_(BAT) _(—) _(MAX). The strategic manager 220determines which of the transmission operating range states areallowable, and determines output torque requests comprising a strategicaccelerator output torque request (‘Output Torque Request AccelStrategic’) and a strategic net output torque request (‘Output TorqueRequest Net Strategic’), all of which are input the operating rangestate analyzer 260 along with system inputs (‘System Inputs’) and powercost inputs (‘Power Cost Inputs’). The operating range state analyzer260 generates a preferred power cost (‘P*cost’) and associated inputspeed (‘N*i’) for each of the allowable operating range states basedupon the operator torque requests, the system inputs, the availablebattery power and the power cost inputs. The preferred power costs andassociated input speeds for the allowable operating range states areinput to the state stabilization and arbitration block 280 which selectsthe preferred operating range state and preferred input speed basedthereon.

FIG. 5 shows the operating range state analyzer 260, which executessearches in each candidate operating range state comprising theallowable ones of the operating range states, including M1 (262), M2(264), G1 (270), G2 (272), G3 (274), and G4 (276) to determine preferredoperation of the torque actuators, i.e., the engine 14 and the first andsecond electric machines 56 and 72 in this embodiment. The preferredoperation preferably comprises a minimum power cost for operating thehybrid powertrain system and an associated engine input for operating inthe candidate operating range state in response to the operator torquerequest. The associated engine input comprises at least one of apreferred engine input speed (‘Ni*’), a preferred engine input power(‘Pi*’), and a preferred engine input torque (‘Ti*’) that is responsiveto and preferably meets the operator torque request. The operating rangestate analyzer 260 evaluates M1-Engine Off (264) and M2-Engine Off (266)to determine a preferred cost (‘P*cost’) for operating the powertrainsystem responsive to and preferably meeting the operator torque requestwhen the engine 14 is in the engine-off state.

FIG. 6 schematically shows signal flow for a 1-dimension search schemethat is preferably executed for each of G1 (270), G2 (272), G3 (274),and G4 (276) to determine the preferred operation. A range of onecontrollable input, in this embodiment comprising minimum and maximuminput torques (‘Ti Min/Max’), is input to a 1-D search engine 415. Theengine power output and thus engine torque input to the transmission 14varies over the range of input speeds Ni. The input speed (‘Ni’) isdetermined in each of the candidate fixed gear operating range statesbased upon the gear ratio, for the transmission output speed No that isinput to the strategic control scheme 310.

The 1-D search engine 415 iteratively generates candidate input torques(‘Ti(j)’) which range between the minimum and maximum input torques,each which is input to an optimization function (‘Opt To/Ta/Tb’) 440,for n search iterations. Other inputs to the optimization function 440include system inputs comprising parametric states related to batterypower, electric motor operation, transmission and engine operation, thespecific operating range state and the operator torque request.

The system inputs include clutch reactive torque capacity, i.e., maximumand minimum clutch reactive torques (‘TCL Min/Max’) for the appliedclutches for the candidate fixed gear operating range state. Inoperation, the input speed (‘Ni’) is combined with a capability of thehydraulic system to generate pressure (‘Pr Main Cap’) (413) to determinea main hydraulic pressure (‘Pmain’). In one embodiment, the controlsystem includes a lookup table stored in memory to determine the mainhydraulic pressure based upon the input speed. FIG. 8 shows thedatagraph that illustrates a capability of an exemplary hydrauliccontrol circuit 42 including the main hydraulic pump 88 to generatehydraulic pressure (‘Pr Main Cap’) based upon the input speed Ni. Thehydraulic control system 42 preferably includes an electrically poweredauxiliary pump (not shown) that generates a minimum hydraulic pressurewhen the input speed is zero, i.e., the engine-off state (‘Ni=0’), andwhen the engine 14 is operating at idle (‘Idle’). When the input speedincreases from zero, e.g., when the engine 14 is spinning, the mainhydraulic pump 88 generates hydraulic pressure. As depicted, thehydraulic pressure in the hydraulic control circuit does not increaseabove the minimum hydraulic pressure until the input speed exceeds theidle speed. When the input speed exceeds the idle speed, the mainhydraulic pump 88 pumps hydraulic fluid to generate hydraulic pressurethat increases with increasing engine input speed, leveling off at amaximum hydraulic pressure (not shown) that can be determined based upona capacity of the specific hydraulic pump.

The control system determines the maximum and minimum clutch reactivetorques (‘TCL Min/Max’) based upon the hydraulic pressure capability(‘Pr Main Cap’) and the operating range state, which determines thespecifically applied clutch(es) (414). In operation, the maximum clutchreactive torque is determined as set forth in the following equation:

TCL_Max=Kn*(P _(MAIN) −P _(RET))   [1]

wherein Kn comprises a scalar gain term describing clutch reactivetorque as a function of pressure gain for the applied clutch,

-   -   P_(MAIN) is the main hydraulic pressure determined based upon        the engine input speed, and    -   P_(RET) is a return spring pressure for the applied clutch.        The minimum clutch reactive torque TCL Min is determined to be a        negative value of the maximum clutch reactive torque.

The optimization function 440 determines transmission operationcomprising an output torque, motor torques, and associated battery andelectrical powers (‘To(j), Ta(j), Tb(j), Pbat(j), Pa(j), Pb(j)’)associated with the candidate input torque based upon the system inputsincluding the maximum and minimum clutch torques in response to theoperator torque request for the candidate operating range state. Theoutput torque, motor torques, and associated battery and electricalpowers and power cost inputs are input to a cost function 450, whichexecutes to determine a power cost (‘Pcost(j)’) for operating thepowertrain at the candidate input torque in response to the operatortorque request. The 1-D search engine 415 iteratively generates thecandidate input torques over the range of input torques. Theoptimization function 440 and the cost function 450 determine powercosts associated with each candidate input torque. A preferred inputtorque (‘Ti*’) and associated preferred cost (‘P*cost’) are identified.The preferred input torque (‘Ti*’) comprises the candidate input torquewithin the range of input torques that results in a minimum power costof the candidate operating range state, i.e., the preferred cost.

The preferred operation in each of M1 and M2 can be determined byexecuting a 2-dimensional search scheme that can be executed in each ofM1 (262) and M2 (264), shown with reference to FIG. 7. FIG. 7schematically shows signal flow for the 2-dimension search scheme.Ranges of two controllable inputs, in this embodiment comprising minimumand maximum input speeds (‘Ni Min/Max’) and minimum and maximum inputpowers (‘Pi Min/Max’) are input to a 2-D search engine 410. The 2-Dsearch engine 410 iteratively generates candidate input speeds (‘Ni(j)’)and candidate input powers (‘Pi(j)’) which range between the minimum andmaximum input speeds and powers. The candidate input power is preferablyconverted to a candidate input torque (‘Ti(j)’) (412). Each candidateinput speed (‘Ni(j)’) is input to a pre-optimization function (418).Other inputs to the pre-optimization function (418) include thehydraulic pressure capability (‘Pr_Main_Cap (Ni)’) and the operatingrange state, as previously described.

The pre-optimization function (418) generates a range comprising maximumand minimum clutch reactive torques (‘TCL Min/Max(j)’) based upon thecandidate input speed Ni(j) (413, 414). Other outputs of thepre-optimization function 418 include a range of motor torques (‘TaMin/Max(j)’, (‘Tb Min/Max(j)’) for the candidate operating point. Theoptimization function 440 determines transmission operation comprisingan output torque, motor torques, and associated battery and electricalpowers (‘To(j), Ta(j), Tb(j), Pbat(j), Pa(j), Pb(j)’) associated withthe candidate input torque (‘Ti(j)’) and candidate input speed(‘Ni(j)’), limited by the range of minimum and maximum input powers fromthe engine 14 to the transmission 10 (‘Pi Min/Max’) and based upon thesystem inputs including the maximum and minimum clutch torques and theoperating torque request for the candidate operating range state. Theoutput torque, motor torques, and associated battery powers and powercost inputs are input to a cost function 450, which executes todetermine a power cost (‘Pcost(j)’) for operating the powertrain at thecandidate input power and candidate input speed in response to theoperator torque request in the candidate operating range state. The 2-Dsearch engine 410 iteratively generates the candidate input speeds andcandidate input powers over the range of input speeds and range of inputpowers and determines the power costs associated therewith to identify apreferred input power (‘P*’) and preferred input speed(‘Ni*’) andassociated preferred cost (‘P*cost’). The preferred input power (‘P*’)and preferred input speed (‘N*’) comprises the candidate input power andcandidate input speed that result in a minimum power cost for thecandidate operating range state.

The power cost inputs to the cost function 450 are determined based uponfactors related to vehicle driveability, fuel economy, emissions, andbattery usage. Power costs are assigned and associated with fuel andelectrical power consumption and are associated with a specificoperating points of the hybrid powertrain. Lower operating costs can beassociated with lower fuel consumption at high conversion efficiencies,lower battery power usage, and lower emissions for each enginespeed/load operating point, and take into account the candidateoperating state of the engine 14. The power costs include engine powerlosses, electric motor power losses, battery power losses, brake powerlosses, and mechanical power losses associated with operating the hybridpowertrain at a specific operating point which includes input speed,motor speeds, input torque, motor torques, a transmission operatingrange state and an engine state.

The state stabilization and arbitration block 280 selects a preferredtransmission operating range state (‘Hybrid Range State Des’) whichpreferably is the transmission operating range state associated with theminimum preferred cost for the allowed operating range states outputfrom the operating range state analyzer 260, taking into account factorsrelated to arbitrating effects of changing the operating range state onthe operation of the transmission to effect stable powertrain operation.The preferred input speed (‘Ni_Des’) is the engine input speedassociated with the preferred engine input comprising the preferredengine input speed (‘Ni*’), the preferred engine input power (‘Pi*’),and the preferred engine input torque (‘Ti*’) that is responsive to andpreferably meets the operator torque request for the selected preferredoperating range state.

The evaluation of candidate input speeds Ni(j) based in part uponhydraulic pressure and correlative minimum and maximum clutch reactivetorques (‘TCL Min/Max(j)’) in the operating range state analyzer 260 isintended to assure that the transmission operation comprising the outputtorque (‘To(j)’) associated with the candidate input torque (‘Ti(j)’) isnot limited by the minimum and maximum clutch reactive torques(‘TCL_Min/Max(j)’) achievable at the candidate input torque.

In operation the control system acts to control the engine input speedNi to control the clutch reactive torque capacity to effect torquetransfer across the applied clutch(es). This can affect system operationat system operating conditions wherein the engine may be in anengine-off state or be operating at slow speeds, and the demand fortorque transfer through the transmission 10 across the appliedclutch(es) exceeds the clutch reactive torque(s) of the appliedclutch(es). Under such operating conditions, the control system can actto increase the engine input speed to increase hydraulic pressure toincrease the clutch reactive torque capacity. Such system operatingconditions can include an operator torque request through theaccelerator pedal 113 wherein the engine is at idle or in the engine-offstate, such as occurs during a vehicle launch. Another system operatingcondition can include system operation at higher speed when an operatortorque request through the accelerator pedal 113 goes to zero includingan input to the brake pedal 112, which can lead to a regenerativebraking operation. Under such operating conditions, the control systemcan act to limit a decrease in the engine input speed to limit adecrease in the hydraulic pressure to maintain the clutch reactivetorque capacity sufficient to effect torque transfer through thetransmission 10 to react with the first and second electric machines 56and 72.

FIG. 9 shows operation of an exemplary system, including a signal inputfrom an accelerator pedal (‘AP’) 113 and input speed Ni and output speedNo (‘No Output Speed’) shown plotted over elapsed time (‘Time’). At apoint in time, system operation changes due to an operator input to theaccelerator pedal 113 comprising a part throttle tip-in (‘Part-ThrottleTip In’), which is the operator torque request used to determine thepredicted accelerator output torque request and the immediateaccelerator output torque request that are inputs to the control systemdescribed beginning with FIG. 3. A first line (‘A’) depicts the inputspeed operation of the engine 14 in response to the input to theaccelerator pedal 113, including a response time delay and withoutcompensation or adjustment for the clutch reactive torque capacity. Theengine input speed in this condition does not spin the hydraulic pump 88sufficiently to generate hydraulic pressure to supply pressurizedhydraulic fluid to the hydraulic control circuit 42 to meet the outputtorque request (‘Input Speed Too Low to Carry Output Torque Request’). Asecond line depicts the input speed operation of the engine 14 inresponse to the input to the accelerator pedal 113, with compensationfor the clutch reactive torque using the control scheme describedhereinabove (‘Pressure Compensated Input Speed’). As depicted, theengine input speed in this condition increases to operate the hydraulicpump 88 to generate sufficient hydraulic pressure to supply pressurizedhydraulic fluid to the hydraulic control circuit 42 to meet the outputtorque request.

It is understood that modifications are allowable within the scope ofthe disclosure. The disclosure has been described with specificreference to the preferred embodiments and modifications thereto.Further modifications and alterations may occur to others upon readingand understanding the specification. It is intended to include all suchmodifications and alterations insofar as they come within the scope ofthe disclosure.

1. Method for controlling a powertrain system including an enginecoupled to an electromechanical transmission to transfer power betweenthe engine and a plurality of torque generating machines and an outputmember, the transmission operative in one of a plurality of operatingrange states through selective application of torque transfer clutchesand the engine operatively coupled to a main hydraulic pump to supplypressurized fluid to a hydraulic circuit operative to apply the torquetransfer clutches, the method comprising: determining an output torquerequest to the output member; determining a pressure output of the mainhydraulic pump based upon an engine input speed; calculating a clutchreactive torque capacity for each applied torque transfer clutch basedupon the pressure output of the main hydraulic pump; and determining apreferred engine input speed to achieve the clutch reactive torquecapacity to meet the output torque request to the output member.
 2. Themethod of claim 1, further comprising determining a preferred operatingrange state for the transmission for the preferred engine input speed toachieve the clutch reactive torque capacity to meet the output torquerequest to the output member.
 3. The method of claim 2, furthercomprising controlling the engine to the preferred engine input speedand controlling the transmission to the preferred operating range stateto achieve the clutch reactive torque capacity to meet the output torquerequest to the output member.
 4. The method of claim 1, furthercomprising: determining the output torque request to the output memberbased upon an operator input to an accelerator pedal; determining apreferred clutch reactive torque capacity to achieve the output torquerequest; and controlling the engine input speed to control the pressureoutput of the main hydraulic pump to achieve the preferred clutchreactive torque capacity.
 5. The method of claim 4, comprisingincreasing the engine input speed to increase the pressure output of themain hydraulic pump to achieve the clutch reactive torque capacity. 6.The method of claim 1, further comprising determining the output torquerequest to the output member based upon an operator input to a brakepedal; determining a preferred clutch reactive torque to achieve theoutput torque request; determining a clutch reactive torque capacity toachieve the preferred clutch reactive torque; and controlling the engineto the preferred engine input speed to control the pressure output ofthe main hydraulic pump to achieve the preferred clutch reactive torquecapacity.
 7. The method of claim 6, comprising maintaining the engineinput speed above a threshold to maintain the pressure output of themain hydraulic pump to maintain the clutch reactive torque capacity toachieve regenerative braking.
 8. The method of claim 1, furthercomprising: executing searches of candidate transmission operating rangestates based upon the preferred engine input speed and the output torquerequest to the output member; and determining preferred motor torquesfor the torque generating machines based upon the preferred engine inputspeed and the output torque request to the output member for thecandidate transmission operating range states.
 9. The method of claim 8,further comprising determining power costs for the transmissionoperations of the candidate operating range states based upon thepreferred motor torques for the torque generating machines and thepreferred engine input speed; and selecting a preferred operating rangestate based upon the power costs.
 10. The method of claim 9, wherein thepreferred operating range state comprises the candidate operating rangestate having a minimum power cost.
 11. The method of claim 9, furthercomprising determining a preferred clutch reactive torque to achieve theoutput torque request; determining a clutch reactive torque capacity toachieve the preferred clutch reactive torque; controlling the engine tothe preferred engine input speed to control the pressure output of themain hydraulic pump to achieve the preferred clutch reactive torquecapacity, and controlling the transmission to the preferred operatingrange state.
 12. The method of claim 11, further comprising controllingthe torque generating machines to the preferred motor torques. 13.Method for controlling a powertrain system including an engine coupledto an electromechanical transmission to transfer power between theengine and a plurality of torque generating machines and an outputmember, the transmission operative in one of a plurality of operatingrange states through selective application of torque transfer clutchesand the engine operatively coupled to a main hydraulic pump to supplypressurized fluid to a hydraulic circuit operative to apply the torquetransfer clutches, the method comprising: determining an output torquerequest to the output member; determining a pressure output of the mainhydraulic pump based upon an engine input speed; calculating a clutchreactive torque capacity for the applied torque transfer clutch basedupon the pressure output of the main hydraulic pump; and controlling theengine to a preferred engine input speed to achieve the clutch reactivetorque capacity and controlling the torque generating machines to meetthe output torque request to the output member.
 14. The method of claim13, further comprising determining a preferred operating range state forthe transmission for the preferred engine input speed to achieve theclutch reactive torque to meet the output torque request to the outputmember.
 15. Method for controlling a powertrain system including ahybrid transmission operative to transfer power between an engine and atorque machine and an output member through application of torquetransfer clutches, the engine operatively coupled to a main hydraulicpump to supply pressurized fluid to a hydraulic circuit operative toapply the torque transfer clutches, the method comprising: determiningan output torque request to the output member; determining a pressureoutput of the main hydraulic pump based upon an engine input speed;calculating clutch reactive torque capacity for the applied torquetransfer clutch based upon the pressure output of the main hydraulicpump; and controlling the engine to a preferred engine input speed toachieve the clutch reactive torque capacity and controlling the torquegenerating machines to meet the output torque request to the outputmember.